Anti-lock-controlled brake system

ABSTRACT

An anti-lock-controlled hydraulic brake system is described having a pump (9) and a master brake cylinder (1). An arrangement for controlling the pump pressure is integrated in the master brake cylinder ( 1 ) and consists of the combination of a connection of the pump to the master cylinder and reservoir, and a primary seal (30, 34) cooperating with a compensating hole (36) in the master cylinder wall. The seal (30, 34) consists of an elastic ring (37) lying on the inside and of a slide ring (38) lying on the outside. The necessary communication between the storage reservoir ( 7 ) and the brake circuits, which enables the brake circuits to be resupplied via a non-return valve, is effected via the nonreturn valves (10, 11) of the pump (9). The double seal can be backed by a secondary seal (41) which completely seals the working chamber against leakage flow past the primary ring seal.

BACKGROUND OF THE INVENTION

This invention is concerned with anti-lock-controlled brake systems inwhich a pump used to supply fluid under pressure during a control cycleis also connected to the master cylinder. Such a brake system is knownfrom German Published Patent Application (DE-OS) No. 36 27 000. Thesystem is characterized in that the pumps, delivering fluid into thebrake circuits during a control operation, directly communicate with theworking chambers of the master brake cylinder. The working pistonsdefining the working chambers are equipped with so-called central valvesworking as pressure control valves, that operate in such a manner as toadjust the pump pressure to be proportional to the pressure generated inthe master cylinder by the brake pedal. The elements of the centralvalves, i.e., the valve body and the valve seat, need to be of ahardened material such as of metal in order to prevent damage during theopening and closing operations, which take place in uninterruptedsuccession during a control operation. Further, the pistons are providedwith sealing cups acting as a non-return valve so as to ensure that, incase of a quick release of the brake, fluid can enter the brake circuitsfrom the storage reservoir via the sealing cups.

There are also known conventional master brake cylinders provided withso-called compensating holes. Directly in front of a sealing cup, theseholes lead into the working chamber of the master brake cylinder fromthe reservoir. With the master brake cylinder not being actuated,communication exists between the brake circuits and the storagereservoir via the compensating hole. Upon actuation of the master brakecylinder, the working pistons are displaced and the sealing cup slidesacross the compensating hole so that the brake circuits will be lockedhydraulically and a pressure build-up will be possible. Such masterbrake cylinders cannot be used in anti-lock-controlled brake systems ofthe above-mentioned type since, with a control of the pump pressureproportional to the brake pedal pressure, the sealing cups would movepast the compensating holes under a high pressure and, in doing so,would be destroyed.

In principle, it would be possible to manufacture the sealing cup of aharder material so that there would be no damage during control cycles.In this case, however, the seal would be unable to perform a nonreturnvalve function as does a soft material sealing cup.

For this reason, master cylinders with central valves in accordance withthe above-mentioned prior art were used in anti-lock-controlled brakesystems. It goes without saying, that the manufacture of such masterbrake cylinders with central valves is considerably more expensive andintricate than that of master brake cylinders for conventional brakesystems.

It is thus an object of this invention to design an anti-lock-controlledbrake system such as to enable the use of a simple master brakecylinder.

SUMMARY OF THE INVENTION

According to the invention, a seal of hardened material is used, and thepump is designed such as to itself provide a flow path for fluid throughthe pump upon a quick release of the brake, with the pump not inoperation. To this end, nonreturn valves which operate as suction anddelivery valves for reciprocating piston pumps are used each valvehaving an extremely low opening pressure. The sealing on the workingpiston of the master brake cylinder can consist either of a combinationof an elastic ring and of a slide ring, with, for instance, the elasticring being made of rubber and the slide ring of Teflon, or a single highShore hardness rubber ring.

This invention also enables a reduction in the bore surface qualityrequirements, to prevent any surface defects from causing a circuitfailure. The invention also compensates for slight leakage occurringwith slide ring sealing, namely the extremely slight leakage in thelow-pressure range.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an antilock controlled brake systemaccording to the present invention with a sectional view of a mastercylinder incorporated therein.

FIG. 2 is a schematic diagram of an antilock controlled brake systemwith a sectional view of a second embodiment of a master cylinderincorporated therein.

DETAILED DESCRIPTION

The antilock controlled brake system shown in FIGS. 1 and 2 consists ofa master brake cylinder 1 with wheel brakes 3 connected thereto via abrake line 2. An inlet valve 4 is in the brake line 2. The wheel brakes3 further communicate with a storage reservoir 7 via a return line 6. Anoutlet valve 5 is inserted into the return line 6. The inlet and outletvalves are electromagnetically operated, the inlet valve 4 being openwhen deenergized, the outlet valve 5 being closed when deenergized. Whenenergized, the valves 4, 5 will change over so that inlet valve 4 willblock the brake line 2 and outlet valve 5 will open the return line 6.The operation of the valves 4, 5 enables fluid under pressure to flowout and to be resupplied to the wheel brakes so that the brakingpressure in the wheel brake is thereby controlled.

By means of a non-illustrated sensor, it is possible to monitor therotational behavior of the wheel, with the sensor signals transmitted toan electronic evaluation unit (not shown) generating operating signalsfor the inlet and outlet valves. The operating signals are formed inaccordance with an algorithm in the manner well known to those skilledin the art, preventing the wheels from locking.

A pump 9 is included in the brake system, the pump 9 drawing fluid infrom the storage reservoir 7, and, via a pressure line 12, deliveringfluid into the brake line 2 between the master brake cylinder 1 and theinlet valve 4. The pump 9 serves to resupply the brake circuit withfluid removed from the wheel brakes during control. Usually areciprocating piston pump is provided for such systems, the pump 9having a suction valve 10 and a delivery valve 11 associated with thepump inlet and outlet respectively. The suction valve 10 is arranged inthe suction line 13 between the storage reservoir 7 and the inlet of thepump 9 and opens towards the pump 9. The delivery valve 11 is in thepressure line 12 between the outlet of the pump 9 and the brake line 2and opens towards the brake line 2. The opening pressure of the nonreturn valves 10, 11 is to be as low as possible, i.e., at a negligibleor minimal opening pressure.

The master brake cylinder itself consists of a housing 20 with alongitudinal bore 21 wherein a floating piston 22 and a push-rod piston23 are slidably mounted in a sealing manner. Floating piston 22 andpush-rod piston 23 are interconnected by means of a coupling unit 24defining the maximum distance between the two pistons. A spring 25 isarranged between the two pistons, keeping them at their maximumdistance.

Return spring 26 is arranged between the end of the bore 21 and thefloating piston 22 and urges the floating piston 22 into its retracted,return position. Within the bore 21, the pistons 22, 23 each define arespective working chamber 39, 40.

Another similar brake circuit may be connected to working chamber 40,such brake circuit being the same as that associated with workingchamber 39.

On its outside edge, the floating piston 22 is provided with an annularchamber 27 communicating permanently with the storage reservoir 7 via ahousing channel 28. The annular chamber 27 is sealed with respect toboth working chamber 40 and working chamber 39. With regard to workingchamber 40, a sealing cup 29 is provided; with regard to chamber 39, adouble primary seal 30 is provided which will be described in moredetail further below. The push-rod piston 23 has a smaller-diameterportion which is passed in a sealing manner through a plug 31 and towhich a pedal is drivingly connected plug 31 partitions off a supplychamber 32 in the housing, the chamber 32 communicating with the storagereservoir 7 via a housing bore 33. Working chamber 40 and supply chamber32 are separated from each other by means of a double primary seal 34 onthe push-rod piston 23.

Double seals 30, 34 are each inserted into a groove located adjacent theend facing the associated working chamber 39, 40 and recessed into theoutside of each respective piston 22, 23. Each seal 30, 34 consists ofan inner first elastic ring 37 of round cross-section (such as ofrubber. Outside the rubber ring 37, there is a Teflon slide ring 38 ofrectangular cross-section. The inner rubber ring 37 is slightlyprestressed and thus pushes the outer ring 38 outwardly against the wallsurface of the bore 21.

In accordance with FIG. 2, the double seals 30, 34 are each insertedinto a first annular groove on the respective piston 22 or 23. Next toeach double seal 30, 34, there is provided a respective secondarysealing cup 41, 42 in an adjacent second groove. The first and secondgrooves lie side by side and are separated from each other by means of arib. The first groove lies nearest to the piston end adjacent therespective working chamber 39, 40. The sealing cups 41 42, are of ausual type, having a lip pressing on the wall of the bore 21 and thusachieving the sealing action.

In the illustrated retracted position of pistons 22 and 23, compensatingholes 36 directly in front of the seals 30, 34, lead into the respectivechambers 39, 40. The compensating holes 36 communicate with the storagereservoir 7. They have a narrow cross-section on the order of 0.8 mm. Itis possible to have an even smaller hole and to provide a plurality ofcompensating holes on the periphery of the housing bore 21.

The system has the following mode of operation:

The symbolically represented pedal being operated, at first the push-rodpiston 23 will be displaced, under the action of spring 25, the floatingpiston 22 also becoming displaced.

The outer rings 38 of the double seals 30, 34 will slide over therespective compensating hole 36 and will thus close communicationbetween the working chambers 39, 40 and the storage reservoir 7. Thebrake circuits will be closed hydraulically so that a pressure may buildup in the brake circuits to brake the vehicle. The nonreturn valve 11 atthe pump outlet will prevent the brake circuit pressure from beingdischarged into the storage reservoir 7.

Upon the release of the brake, the pistons 22 and 23 will be displacedto the right (see drawing) under the action of return springs 25 and 26.During this action there may form a vacuum in the system so that fluidwill be drawn from the storage reservoir 7 into the brake circuits viathe non return valves 10 and 11 of the pumps 9. As soon as the pistons22, 23 have reached their return positions, the compensating holes 36will be opened so that, with the brake not applied, the brake circuitswill communicate with the storage reservoir 7.

During a braking operation, the pressure may increase to a level causingwheel lock-up. The brake system will then switch into the anti-lockcontrol mode, in which the motor driving the pump 9 is activated. Viapressure line 12, pump 9 delivers fluid from the storage reservoir 7into the brake circuit, thereby causing fluid under pressure to flow toworking chambers 39 and 40.

The pistons 22, 23 are displaced, against the pedal actuating force,back to their return positions until the compensating holes 36 areuncovered. Excess fluid will now escape into the storage reservoir 7 viacompensating hole 36. In doing so, the pressure in the working chamberswill be reduced so that, under the action of the pedal pressure, thepistons will again be displaced to the left, the compensating holes 36again being blocked. Since the pump 9 will continue to deliver, thepistons 22, 23 will again be reset, the compensating holes 36 againopened. This operation will repeat itself in quick succession so that,in the end, there will result a flow metering, with that much fluidbeing discharged via compensating hole 36 as will be delivered by pump 9into the working chambers 34, 40 of master brake cylinder 1. Theadjusted pressure will correspond to the pedal pressure.

In order to prevent the slide rings 38 from being damaged they must havea certain hardness. The same must be chosen so as to ensure that even arepeated sliding past the compensating hole 36 will not cause anydamages to the slide ring sealing 38.

The additional sealing cups as per FIG. 2 will perform the followingtask. Because of its hard surface structure, the slide ring of thedouble seal cannot perfectly seal the working chamber 39, 40. There willthus always be a small leakage. In case of damage to the slide ringsealing or to the wall of the bore 21 there may also be a major flow offluid past the slide ring sealing. The secondary seals 41, 42 are thusarranged behind the double seals to insure that the working chamber 39,40 will be sealed completely and prevent any significant volume ofleakage flow from being removed completely from the associated brakecircuit and from entering respectively annular chamber 27 orcompensating chamber 32. The pressure in the area between the two sealswill not be very great as the leakage will generally be small, thus thesealing cup overriding compensating hole 36 under but a small pressure.Any damage to the seal will thus be avoided. This arrangement has afurther advantage in that there is no need for an extremely smoothsurface treatment of the wall of the bore 21 as a certain leakage flowalong the double seal can be tolerated. The inner and outer rings 37, 38may be combined into one ring of a high Shore hardness.

I claim:
 1. An anti-lock-controlled brake system including at least one wheel brake, a brake pedal, a master brake cylinder having a housing with an internal bore formed therein, at least one working piston and one working chamber, said working chamber defined in part by one end of said working piston and by said internal bore, said working piston slidably movable in said master cylinder housing, said internal bore of said brake pedal engaged with said working piston, a return spring acting on said working piston in opposition to said brake pedal engagement, said working piston movable towards and away from a retracted position by actuation by said brake pedal and return by said return spring, a storage reservoir, means for communicating said working chamber with said reservoir, including a valve arrangement opening communication when said master brake cylinder is not operated, and closing said communication when said master brake cylinder is operated, a controllably operable pump having a suction side inlet connected to said storage reservoir and a delivery side outlet connected to said working chamber and said at least one wheel brake, a brake line connected to said working chamber and said pump outlet and said wheel brake and a return line connecting said reservoir to said wheel brake, an inlet valve associated with said wheel brake and controlling communication of said wheel brake with said working chamber and pump outlet via said brake line and an outlet valve controlling communication of said reservoir and said wheel brake via said return line and enabling a slip-dependent wheel brake pressure control, said valve arrangement including a primary seal provided on said working piston and retained in an external groove in said working piston adjacent said one end thereof defining said working chamber, said seal comprised of an inner first elastic ring and of an outer second ring of harder material, said outer second ring expanded by said inner first ring to engage said internal bore in said master brake cylinder housing to be in sliding engagement therewith as said working piston is moved in said bore; a narrow hole in said master cylinder directly leading into said working chamber, located just ahead of said seal when said working piston is in said retracted position to allow flow through said narrow hole and past said one end of said piston into said working chamber; said pump open to free fluid flow therethrough from said reservoir to said working chamber when said pump is not operated and said brake pedal is released.
 2. A brake system as claimed in claim 1, wherein said pump has a suction valve and a delivery valve associated with said inlet and outlet, each of said suction valve and said delivery valve being non-return valves with a minimal opening pressure.
 3. A brake system as claimed in claim 1, wherein said inner first ring is of rubber and said outer second ring is of Teflon.
 4. A brake system as claimed in claim 3, wherein said inner first ring has a circular cross-section and said outer second ring has a rectangular cross-section.
 5. A brake system as claimed in claim 1, further including a second seal disposed in a second groove recessed into said working piston, said second groove adjacent to said external groove but away from said piston one end defining said working chamber.
 6. A brake system as claimed in claim 5 wherein said second seal comprises an elastic seal.
 7. An antilock brake system comprising at least one hydraulically operated wheel brake, a brake pedal, a master cylinder having a housing formed with a bore, a piston slidably disposed in said bore defining with one end thereof a working chamber, said piston operatively connected to said brake pedal to be able to be stroked away from a retracted position, said bore to an advanced position, return spring means for returning said piston to said retracted position in said bore, a brake line connecting said master cylinder working chamber to said wheel brake, an inlet valve in said brake line for controlling communication between said working chamber and said wheel brake, a reservoir, a return line extending between said wheel brake and said reservoir for return fluid flow, an outlet valve in said return line controlling communication between said reservoir and said wheel brake, pump means able to be operated to pressurize fluid, said pump means having an inlet connected to said reservoir and an outlet connected to said brake line at a point between said working chamber and said inlet valve, a first one way valve connected to said pump means inlet opening only towards said pump means and a second one way valve connected to said pump means outlet opening only towards said brake line, said first and second one way valves having a negligible opening pressure, a primary seal on said piston adjacent said one end defining said working chamber, said primary seal slidably engaging said master cylinder, a compensating hole entering through said master cylinder bore at an axial location to be just opened directly into said working chamber when said piston moves to said retracted position in which said one end thereof is withdrawn past said compensating hole to allow flow from said reservoir through said compensating hole and past said piston one end and into said working chamber, and a fluid connection between said reservoir and said compensating hole, said pump means open to free fluid flow therethrough in the opening direction of said first and second one way valves when said pump means is not operated and said brake pedal is released, whereby said piston seal and said compensating hole can act to meter flow out of said working chamber to said reservoir when said working chamber is pressurized by said pump means to adjust said pump means pressure to said working chamber pressure level developed by said brake pedal.
 8. The antilock brake system according to claim 7 wherein said primary seal includes a relatively hard outer ring and elastic means urging said hard outer ring outwardly to engage said master cylinder bore.
 9. The antilock brake system according to claim 8 wherein said outer ring comprises a plastic ring and further including an elastic inner ring comprising said means urging said outer ring outwardly.
 10. The antilock brake system according to claim 7, wherein said primary seal comprises a ring of relatively hard material and further including a secondary seal comprising a ring of relatively softer material axially spaced from said primary seal in a direction away from said one end of said piston.
 11. The antilock brake system according to claim 7, wherein said compensating hole is of a size on the order of 0.8 mm in diameter. 